In these co-pending applications, in vivo telemetric pressure sensing devices, systems and methods were described for which the sensor, once implanted in the body, could be interrogated telemetrically by means of any of a variety of physical principles, and it could be calibrated in vivo by pressing on the skin above the sensor so as to drive the sensor's diaphragm means or associated movable elements against a stop within the sensor, as indicated by a telemetric signal or response of the device at or near the stop position. Further, by pressing on the skin with a pressure cuff or force applicator until the stop position was achieved, which corresponds to a balance of pressure across the sensor, the internal pressure could be measured without need for a calibration of the sensor prior to implantation. Thus, the approach is one where no wires or tubes need to penetrate the skin, and one can get an accurate pressure reading by calibrating the device in vivo using a null pressure or pressure balancing method across the intact skin. As stated in my several papers on the subject, including: A Pressure-Balanced Radio Telemetry System for the Measurement of Intracranial Pressure, J. Neurosurgery 47 899-911 (1977), and, A Telemetric Pressure Sensor for Ventricular Shunt Systems, Surg. Neurol. 11, 287-294 (1979), the method is the analog of measuring blood pressure by the sphygmomanometric method, except that an implanted pressure sensing device is used in the former in place of the natural arteries in the latter.
My previous applications stated that there are a multitude of ways of telemetrically detecting that the sensor's movable diaphragm or cooperatively connected movable elements are at or near their stop or balanced position: "This equilibrium condition or balanced position of the movable element is detected with an external detection system by means of electromagnetic, acoustic, radiation, mechanical, or other methods of coupling across the skin to the implanted sensor"; and, "A displacement of 6 (movable element) relative to 5 (a relatively fixed portion of the sensor) can be made to cause changes in some physical, electrical, or magnetic characteristic of the sensor." Some specific examples of the changeable detectable characteristic or detectable parameter were given including the resonant frequency of an electrical circuit, movements of the diaphragm means or associated movable elements to be detected by acoustic, ultrasonic, echo-reflection, doppler shift or other scattering means. However, it was stated that these diverse means of telemetric detection and diverse types of physical characteristics are subsumed under the general concept of the invention appraoch, namely of seeking a balance condition of the sensor and applying a variable, known external pressure to the intact skin over the sensor and simultaneously detecting the occurrence of the balance condition by one of a diverse number of telemetric means as one varies the external pressure through the balance condition.
In this continuation-in-part application, several other examples of specific telemetric detection means, specific aspects of the associated external detection apparatus and specific means of the implanted sensor having a detectable parameter or detectable characteristic are described in more detail. In particular, acoustic coupling of the detection apparatus, to the implanted sensor means of producing an acoustic response of the implanted sensor at or near the balance position or stop position of the diaphragm means, and means of converting a non-acoustic characteristic response parameter of the implanted sensor to an acoustic response through apparatus cooperatively connected to the external detection apparatus will be described. Associated inventions will then be claimed. The production of an acoustic signal or response to indicate, to the person measuring the pressure, that the balance condition of the implanted sensor has been reached, as he is simultaneously varying the cuff pressure so as to search for the balanced pressure condition, makes the analogy of the pressure-balanced telemetric method of the previous application even closer to that of convention, time-tested sphygmomanometric blood pressure measurements. In the latter, in its simplest form, a stethoscope is held on the skin near a pulsating blood artery, and a pressure cuff is inflated on the skin to gradually occlude the artery. This is analogous to driving the implanted sensor to its stop position. One listens to the artery pulsations until they stop, at which point the cuff pressure equals the maximum blood pressure, which is visualized on the cuff's pressure guage in the pressure balanced telemetric method, by similarly converting the implanted pressure sensor's response characteristic at the balance point to an audible acoustic response, one frees the operator from having to watch a visual indicator of the balance condition, and he can merely watch the cuff pressure gauge. This can be an aid and a convenience in making the measurement, and there are diverse ways of implementing the acoustic, telemetric, pressure-balancing method as will be illustrated in several examples below.